Someone mentioned using SS coachscrews from Bunnings as glue in bolts. I just wanted to know if anyone has an opinion on the quality of these. The SS coachscrews at bunnings that I found have 'A2 and THE' stamped on the head. I thought they had to have A2-70 or similar as well as THE.

No. You can tighten them too much and they could be ready to snap. I use coach screws alot but never as a permanent solution for protection and certainly not as a climbing anchor. Others may disagree. The problem with the markings you mention is that they could well be a glue in machine bolt and people will think they are and actually trust them!!! dont be a stooge , place glue ins.

I just realised you wrote 'as' glue ins. Why not use a machine bolt? I reckon the big bunnings might sell them , just give them some extra grinding and notching. Now that I realise you want to glue the coach screw in its probably ok , they usually have quite deep thread which might compromise the diameter of the bolt?

I reckon just don't use them as permanent bolts. They are no where near as strong as machine bolts. If you don't believe me get one and try screwing it into a hardwood post. They snap really easily. Then try putting a machine bolt into some nuts in a vice and tighten it up. No way you will snap it, regardless of the leverage you use.
I've used ss coach screws building and you need to make sure they are predrilled properly or they snap surprisingly easily.
G

On 29/07/2014 Mr Poopypants wrote:>I reckon just don't use them as permanent bolts. They are no where near>as strong as machine bolts. If you don't believe me get one and try screwing>it into a hardwood post. They snap really easily.

They snap?! How? I don't see how they could be weaker than a similar sized machine bolt when used as a glue-in.

I've used quite a few of those coach-screws as glue in carrots in the last year. There are two reasons I have used them instead of normal machine bolts, they don't require additional grinding (the thread is wide, deep and goes almost all the way to the top of the bolt) and the second reason is cost. They are half the price of a normal machine bolts (something like $1.50 per bolt at Bunnings).

You will need to grind off the edges of the hex-head so PFH bolt brackets will fit.

The el cheapo Bunnings (or other) SS Coach bolts, if they have A2 on them, may be grade A2-50. These have approx 30% less capacity than A2-70 grade and are considerably more maleable, ie the metal stretches more easily. A2-50 elongates 50% more than A2-70 (regular strength for fixings). This may explain why the heads can be snapped off far more easily.

On 29/07/2014 The good Dr wrote:>The el cheapo Bunnings (or other) SS Coach bolts, if they have A2 on them,>may be grade A2-50. These have approx 30% less capacity than A2-70 grade>and are considerably more maleable, ie the metal stretches more easily.>A2-50 elongates 50% more than A2-70 (regular strength for fixings). This>may explain why the heads can be snapped off far more easily.

Do they warp visibly before breaking? I have snapped a lot of carrots off when rebolting - most of the time you can twist the head about 90 degrees before it snaps. This obviously never happens in a climbing fall. I've done pull out tests (using Mikls bolt tester) with these SS coachscrews and saw no sign of bolt damage. The rock or glue failed way before any bolt warping at well over a tonne.

>Neil, I thought you were not placing glued in carrots any more.

As I said above - I have been using them mostly with Fixed Hangers, but I have placed a few as top belay anchors at Point Perp that require keyhole hangers (as is the usual practice at that cliff to hide belay bolts from tourists)

I guess Neils point is they snap when twisted just as a machine bolt will but if they are GLUED IN as opposed to screwing them into a hole they will function just as effectively as a machine bolt so long as the quality of metal is equivalent. I use fully threaded machine bolts sometimes , while we are on the subject what is the danger in using fully threaded MB? I imagine they would reduce diameter from 10mm nearer to 8mm , and this would not be as strong? I know optimally there should be no thread within 25mm of surface but I have seen and used plenty of glue-in 316 MB's with a full thread on various climbs and anchors and they hold up ok.

>I've stopped using coach bolts when building because I don't trust their>strength. As mentioned, they snap very easily.

Yes you can break them when over-tightened or the hole is too small / short. I use soap or tallow on the thread to help them go in, especially in old dry hardwood: in this case the pilot hole diameter should allow less than 1mm of the thread to bite — holds good & no snapping. Stainless steel is less ductile than standard galvanised coach screws. If breaking under big loads you need to go up in diameter.

In terms of raw strength you shouldn't have any problems with any steel/stainless steel 10mm bolts. Even "soft" 50 grade has close to a 40kN shear strength. The bigger concern is quality control of the fabrication of the bolts that may not have been meant for structural purposes.

If you are shearing bolts off from over tightening then that is user error. Any bolt will snap if over torqued.

I had this problem on a large construction site where we did thousands of fixings. Buy your coach bolt/screw from somewhere other than bunnings. We did random sample tests of 20 screws from differing suppliers. Best comparison for quality was weight. Cup and cone failure just under head even at low torque was common in cheapest bolts. We determined that with cheapest bolts 20 - 30% of bolt heads would have their strength (elastic limit) reduced during fixing with little outward signs and hence not comply with fixing specification.
Grooving of machine bolts also introduces stress concentrator s and if done poorly localised heat stress.
My view -,pay more for quality coach screw with wide thread from fastener dealer and not a general hardware warehouse.

Well, I've snapped dozens of them, just using a ring spanner, and as anyone who knows me will attest - I have the arms of Monty Burns (not Neil Monty). Sure, I've also snapped old carrots even easier sometimes. I just think a new bolt should be stronger than that!
Over torqued / talked?? Glued in they are probably okay in shear, but I wouldn't go out of my way to put them in!
As for any bolt breaking if over-torqued - I'd like to see anyone break a 10mm rated stainless machine bolt torquing it with a ring spanner!!! Not going to happen.
Except for Wolfy - Wolfy could do it.
:-)